1. Technical Field
The present invention relates to an x-ray generating apparatus.
2. Description of the Related Art
X-ray generating apparatuses of a type that causes electrons to collide with a target in a vacuum container and generates x-rays include one using a reflection target that removes the x-rays in a different direction from the travel direction of the electrons, and one using a transmission target that removes the x-rays in substantially the same direction as the travel direction of the electrons.
Of them, the reflection target generally uses a bulk material. The reflection target is placed, some distance away from an x-ray irradiation window for removing x-rays from the vacuum container to the outside, in the rear of the container. In contrast, the transmission target generally adopts a structure of being laminated and formed integrally with the x-ray irradiation window. Accordingly, an x-ray focal spot is at the nearest position to the x-ray irradiation window. Accordingly, there is an advantage that the transmission target can increase a fluoroscopic magnification by being used in an apparatus that constructs a fluoroscopic image and a tomogram. However, conversely, the transmission target is laminated and formed into a thin film on one side of the x-ray irradiation window. Accordingly, there is a problem that the life of the transmission target is reduced by thermal damage due to electron irradiation.
For the purpose of increasing the life of such a transmission target, for example, JP-A-2000-90862 proposed to move a target freely to change a position to be irradiated with electrons on a target surface. JP-A-2000-90862 discloses a technology for, in an x-ray generating apparatus that uses an open vacuum container and includes a transmission target, moving the target via an O-ring and a vacuum bellows.
In the above proposal, FIG. 8 is a schematic cross-sectional view illustrating a configuration in a case of using a rubber O-ring. In an open-transmissive x-ray generating apparatus configured to accommodate, in a vacuum container 501, an electron gun 502 including an electron source and a group of electrodes for accelerating and focusing electrons from the electron source to freely evacuate the vacuum container 501 by a vacuum pump 503, an x-ray irradiation window 505 where a target 504 is integrally laminated and formed is mounted on the vacuum container 501 via an O-ring 506, and is rotationally moved at a position that is eccentric with respect to, for example, the track of an electron beam B from the electron gun 502. Accordingly, the position of irradiation of the electron beam B on the surface of the target 504 is changed.
However, if a rubber O-ring is used as described above, the degree of vacuum decreases gradually due to the gas transmission of the O-ring, and the evaporation of vacuum grease and the like. Hence, as in FIG. 8, it is effective against an open apparatus that always exhausts air by a vacuum pump such as a turbo-molecular pump. However, it is not possible to be applied to an x-ray generating apparatus using a seal-off vacuum container such as illustrated in FIG. 9, that is, a sealed x-ray generating apparatus. In other words, in the sealed apparatus illustrated in FIG. 9, an x-ray irradiation window 605 where a target 604 is integrally laminated and formed cannot maintain the degree of vacuum unless airtightly fixed by welding or brazing to a vacuum container 601 where an electron gun 602 is accommodated.
A structure where part of the vacuum container, together with the target and the x-ray irradiation window, is moved via the vacuum bellows can be applied to such a sealed apparatus. A configuration example of the case where the vacuum bellows is used is described based on FIG. 10 that is a schematic cross-sectional view of enlarged main parts in the vicinity of a target. In this example, a through hole 701a is formed in the top of a main body 701 of the vacuum container that accommodates an electron gun (not illustrated) and is fixed to an apparatus frame or the like. One end (lower end) of a vacuum bellows 702 is airtightly fixed to the periphery of the through hole 701a by welding or brazing. In addition, the other end (upper end) of the vacuum bellows 702 is airtightly fixed likewise to the periphery of a recess 703a that is formed in a moving member 703 and opens downward.
An x-ray irradiation window 705 where a target 704 is laminated and formed is fixed to the moving member 703 in such a manner as to form a ceiling portion of the recess 703a. Therefore, a wall body of the main body 701 of the vacuum container, and the vacuum bellows 702 of which lower end communicates with the main body 701 and of which upper end is blocked by the x-ray irradiation window 705 serve as a wall body partitioning the inside and the outside of the vacuum container. An inner region V of them enters a vacuum state.
The electron beam B from the electron gun is applied from the main body 701 to the target 704 through the through hole 701a and the inside of the vacuum bellows 702. Consequently, the vacuum bellows 702 is bent to move the moving member 703. Accordingly, the position of irradiation of the electron beam B of the target 704 can be changed.
When, for example, an x-ray generating apparatus of this type is used for an x-ray test apparatus or the like, if space coordinates of an x-ray focal spot are changed, even if a sample is placed at the same location, a fluoroscopic region is changed. In addition, various readjustments such as reconfiguration of various parameters of an apparatus system and an adjustment to the position of an apparatus component are required, which is not preferable.
Therefore, in the configuration of FIG. 10, it is required to restrict the movement of the moving member 703 only to a direction orthogonal to the direction of irradiation of the electron beam B, that is, to prevent the target 704 from moving and inclining in an approaching/separation direction with respect to the electron gun. Therefore, in FIG. 10, a contact member 707 for guiding and the like are provided to the main body 701 to cause the moving member 703 to be displaced while coming into sliding contact with the contact member 707.
In the configuration of FIG. 10, a strong force acts on the vacuum bellows 702 in a direction of its contraction due to the pressure difference between the inside and the outside, that is, a direction toward the main body 701. Therefore, a strong frictional force works on a sliding surface between the contact member 707 on the main body 701 side and the moving member 703. Accordingly, it becomes impossible to move the moving member 703 easily. It becomes a practical problem. In order to solve the problem, it is also conceivable to apply a lubricant to the sliding surface. However, it is difficult to cause the movement with the same force for a long period of time.
Moreover, as described above, the x-ray generating apparatus using a transmission target is advantageous on the respect of being able to increase the fluoroscopic magnification, as compared to one using a reflection target. However, in order to achieve this, it is required to place an object at a position close to the x-ray irradiation window. Hence, providing a large structure near the x-ray irradiation window should be avoided as much as possible. In addition, it is not possible either to provide a space for reducing a sliding frictional force in a guide mechanism for regulating the displacement of the moving member with respect to the main body of the vacuum container.
The present invention has been made considering such circumstances. An objective of the present invention is to provide an x-ray generating apparatus that can easily displace a moving member that holds a target and an x-ray irradiation window with respect to a main body of a vacuum container with a light force with a compact mechanism, and can extend the life of the target without impairing an advantage being a high fluoroscopic magnification that can be obtained by using a transmission target.